Serpentine

Hardness: 2.5-5 (Mohs scale); Color: Various shades of green (light to dark, olive, yellowish-green, brownish-green), sometimes with mottled or spotted patterns; Luster: Greasy, waxy, silky (chrysotile), or dull; Crystal structure: Usually massive, fibrous (chrysotile), platy (lizardite), or micaceous (antigorite); Cleavage: None to indistinct; Specific Gravity: 2.5-2.6

Formed through the metamorphism of ultramafic igneous rocks (rich in olivine and pyroxenes) through a process called serpentinization. This occurs when these rocks react with water at low to moderate temperatures, typically in oceanic or subduction zone settings. The geological age can vary widely depending on the original rock and the metamorphic event.

Industry: Dimension stone, decorative stone (known as 'verde antique' marble), building facings, insulation (asbestos varieties, though now largely restricted due to health concerns). Jewelry/Ornamental: Carving material (e.g., bowls, small sculptures), beads, cabochons due to its attractive green color and ability to take a polish. It's often mistaken for jade.

The name 'serpentine' comes from the Latin 'serpens' meaning snake, referring to its typically mottled, green color which often resembles a serpent's skin. Some varieties of serpentine contain chrysotile asbestos, a fibrous mineral known for its heat resistance and insulating properties, but also its health risks when inhaled. It is the state rock of California.

In the field, serpentine is identified by its characteristic greasy or waxy feel, shades of green color, and often mottled appearance. It can be found in mountain ranges, ophiolite complexes (sections of oceanic crust and upper mantle thrust onto continental crust), and areas with extensive faulting and tectonic activity. Common locations include the Appalachian Mountains, California, Italy, and New Zealand. Collectors often look for attractive patterns and colors, and may seek out specific varieties like bowenite (a hard, translucent serpentine often used in carvings).